Mount Vesuvius is a volcano located in southern Italy, near the bay of Naples
and the city of Naples. It is the only active volcano on the European mainland.
Vesuvius rises to a height of 1277 m (4190 ft). Vesuvio (Vesuvius) is probably
the most famous volcano on earth, and is one of the most dangerous. Mount
Vesuvius is a strato-volcano consisting of a volcanic cone (Gran Cono) that was
built within a summit caldera (Mount Somma).
The Somma-Vesuvius complex has
formed over the last 25,000 years by means of a sequence of eruptions of
variable explosiveness, ranging from the quiet lava outpourings that
characterized much of the latest activity (for example from 1881 to 1899 and
from 1926 to 1930) to the explosive Plinian eruptions, including the one that
destroyed Pompeii and killed thousands of people in 79 A.D. At least seven
Plinian eruptions have been identified in the eruptive history of Somma-Vesuvius
(1). Each was preceded by a long period of stillness, which in the case of the
79 A.D. eruption lasted about 700 years.
These eruptions were fed by viscous
water-rich phonotitic to tephritic phonolitic magmas that appear to have
differentiated in shallow crustal conditions. They are believed to have slowly
filled a reservoir where differentiation was driven by compositional convection.
A minimum depth of about 3 km was inferred for the top of the magmatic reservoir
from mineral equilibria of metamorphic carbonate ejecta (2). Fluid inclusions
(CO.sub.2 and H.
sub.2O-CO.sub.2) in clinopyroxenes from cumulate and
nodules indicate a trapping pressure of 1.0 to 2.5 kbar at about 1200 degreesC,
suggesting that these minerals crystallized at depths of 4 to 10 km (3).
differentiated magma fraction was about 30% of the total magma in the reservoir,
and a volume of about 2 to 3 km.sup.3 was inferred for the reservoir (4). The
magma ascent to the surface occurred through a conduit of possibly 70 to 100 m
in diameter (5). A thermal model predicts that such a reservoir should contain a
core of partially molten magma (6) that can be detected by high-resolution
seismic tomography. The earliest outcropping volcanic deposits date back to
about 25,000 years ago.
The lavas observed at a -1125 m bore-hole are about
0,3-0,5 million years old. It is known for the first eruption of which an
eyewitness account is preserved, in 79 AD. Geologically, Vesuvio is unique for
its unusual versatility. Its activity ranging from Hawaiian-style release of
liquid lava, fountaining and lava lakes, over Strombolian and Vulcanian activity
to violently explosive, plinian events that produce pyroclastic flows and
surges. Vesuvius is a complex volcano. A complex volcano is "an extensive
assemblage of spatially, temporally, and genetically related major and minor
volcanic centers with there associated lava flows and pyroclastic flows.
Vesuvius has a long history. The oldest dated rock from the volcano is about
300,000 years old. It was collected from a well drilled near the volcano and was
probably part of the Somma volcano. After Somma collapsed about 17,000 years
ago, Vesuvius began to form. Four types of eruption have been documented: a)
Plinian (AD 79, Pompeii type) events with widespread air fall and major
pyroclastic surges and flows; b) sub-Plinian to Plinian, more moderately sized
eruptions (AD 472, 1631) with heavy tephra falls around the volcano and
pyroclastic flows and surges; c) small to medium-sized, Strombolian to Vulcanian
eruptions (numerous events during the 1631-1944 cycle, such as 1906 and 1944)
with local heavy tephra falls and major lava flows and small pyroclastic
avalanches restricted to the active cone itself. The fourth type it is the
smallest of all eruption types observed at Vesuvio.
It is the persistent
Strombolian to Hawaiian style eruption that characterizes almost all of an
eruptive sub-cycle, such as was the case during the period 1913-1944. Activity
of this kind is mainly restricted to the central crater where one or more
intracrateral cones form, and to the sides of the cone. Lava flows from the
summit crater or from the sub terminal vents extend beyond the cone’s base. A
somewhat particular kind of persistent activity is the slow release of large
amounts of lava from sub terminal fractures to form thick piles of lava with
little lateral extension, such as the lava cupola of Colle Umberto, formed in
1895-1899. (7) Vesuvius lies over a subduction zone. The two plates are the
African plate and the Eurasian plate.
The African plate is moving northward at
about one inch (2-3 cm) per year and is slowly closing the Mediterranean basin.
As it moves to the north, .